This invention relates generally to mirror angle control apparatuses, and more particularly to a mirror angle control apparatus for controlling an angle of a mirror surface of an electric mirror assembly provided on a vehicle as a door mirror, a fender mirror and the like.
In general, the electric mirror assembly used for a door mirror, a fender mirror or the like in a vehicle accommodates a mirror angle control apparatus which includes a vertical motion driving motor for adjustment of mirror surface orientation upward or downward, a lateral motion driving motor for adjustment of the mirror surface orientation rightward or leftward, and a controller for controlling the number of rotations of each of these driving motors.
The applicant has previously devised, and disclosed in Japanese Laid-Open Patent Application, Publication No. 2001-138812 A, one example of the mirror angle control apparatuses for a vehicular electric mirror assembly, which includes a driving motor comprised of a direct-current brush motor, a motor signal detection means for outputting a pulse signal generated as a result of waveform shaping of a high-frequency motor brush switching signal detected by a pickup coil connected in series with the driving motor, and a pulse signal count means for counting the pulse signal to thereby detect and control the number of rotations of the driving motor.
In this example, since the driving motor is comprised of a direct-current brush motor, the wearing away of the brush, the defective condition in brush contacts, or like circumstance is likely to occur, and thus generates a disadvantageously reduced signal level of the motor brush switching signal. In such a case, the motor brush switching signal cannot be properly wave-shaped, so that a momentary loss (so-called “dropout”) of the pulse signal may occur. This resultantly makes it impossible to accurately control the number of rotations of the driving motor, which disadvantageously reduces the accuracy in mirror angle control or adjustment of mirror surface orientation.